Weighted elastomers, cement compositions comprising weighted elastomers, and methods of use

ABSTRACT

Methods and compositions are provided that relate to weighted elastomers. The weighted elastomers may comprise an elastomer and a weighting agent attached to an outer surface of the elastomer. An embodiment includes a method of cementing that comprises providing a cement composition containing cement, water, and a weighted elastomer. In addition, the cement composition may be introduced into a subterranean formation and allowed to set therein.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.12/821,514, entitled “Weighted Elastomers, Cement CompositionsComprising Weighted Elastomers, and Methods of Use,” filed on Jun. 23,2010, which is a continuation-in-part of U.S. patent application Ser.No. 12/511,793, entitled “Weighted Elastomers, Cement CompositionsComprising Weighted Elastomers, and Methods of Use,” filed on Jul. 29,2009, the entire disclosures of which are incorporated herein byreference.

BACKGROUND

The present invention relates to weighted elastomers and, moreparticularly, in certain embodiments, to weighted elastomers, cementcompositions comprising weighted elastomers, and methods of usingweighted elastomers in cementing operations.

Cement compositions may be used in a variety of subterraneanapplications. For example, in subterranean well construction, a pipestring (e.g., casing, liners, expandable tubulars, etc.) may be run intoa well bore and cemented in place. The process of cementing the pipestring in place is commonly referred to as “primary cementing.” In atypical primary cementing method, a cement composition may be pumpedinto an annulus between the walls of the well bore and the exteriorsurface of the pipe string disposed therein. The cement composition mayset in the annular space, thereby forming an annular sheath of hardened,substantially impermeable cement (i.e., a cement sheath) that maysupport and position the pipe string in the well bore and may bond theexterior surface of the pipe string to the subterranean formation. Amongother things, the cement sheath surrounding the pipe string shouldfunction to prevent the migration of fluids in the annulus, as well asprotecting the pipe string from corrosion. Cement compositions also maybe used in remedial cementing methods, for example, to seal cracks orholes in pipe strings or cement sheaths, to seal highly permeableformation zones or fractures, to place a cement plug, and the like.

Elastomers are one additive that may be included in a cementcomposition. Among other reasons, elastomers may be included in a cementcomposition to improve the mechanical properties of the set cementcomposition. For example, elastomers may be included in a cementcomposition to improve the elasticity and ductility of the set cementcomposition, thereby potentially counteracting possible stresses thatmay be encountered by the cement composition in a well bore. In someinstances, elastomers that swell upon contact with water and/or oil maybe used. These swellable elastomers may help maintain zonal isolation,for example, by swelling when contacted by oil and/or water to sealcracks in the cement sheath and/or micro-annulus between the cementsheath and the pipe string or formation that may be created.

Weighting agents also may be included in the cement compositions toincrease the density of the cement composition. A cement compositionhaving an increased density may be desirable, for example, in deep wellswhere high pressure may be encountered. Examples of weighting agentsthat may be used include, but are not limited to, hematite, hausmannite,barite, and sand.

A problem often encountered when both elastomers and weighting agentsare included in a cement composition is that the elastomers andweighting agents tend to segregate in different areas of the cementcomposition. For example, the weighting agents generally tend to sinkwhile the elastomers tend to float, which can leave certain areas withlittle or no weighting agent and other areas with little or noelastomer. As a result, the cement composition may not have a uniformdensity distribution when introduced into the formation, resulting in apotential for the design specifications of the cement composition to notbe met. To prevent this undesired segregation, great care is often takenin formulating cement compositions that comprise both elastomers andweighting agents. This may result in added expense and complexity dueto, among other things, a need for additional additives and monitoring.

SUMMARY

The present invention relates to weighted elastomers and, moreparticularly, in certain embodiments, to weighted elastomers, cementcompositions comprising weighted elastomers, and methods of usingweighted elastomers in cementing operations.

An embodiment of the present invention may comprise a weightedelastomer. The weighted elastomer may comprise an elastomer and aweighting agent attached to an outer surface of the elastomer. Theweighted agent may comprise a material selected from the groupconsisting of pumicite, perlite, and a combination thereof. The weightedelastomer may have a specific gravity of at least about 1.1.

Another embodiment of the present invention may comprise a cementcomposition. The cement composition may comprise cement, water, and aweighted elastomer. The weighted elastomer may comprise an elastomer anda weighting agent attached to an outer surface of the elastomer. Theweighted agent may comprise a material selected from the groupconsisting of pumicite, perlite, and a combination thereof.

Another embodiment of the present invention provides a method ofcementing. The method of cementing may comprise providing a cementcomposition that comprises cement, water, and a weighted elastomer. Theweighted elastomer may comprise an elastomer and a weighting agentattached to an outer surface of the elastomer. The weighted agent maycomprise a material selected from the group consisting of pumicite,perlite, and a combination thereof. The method of cementing further maycomprise allowing the cement composition to set.

Yet another embodiment of the present invention provides a method thatmay comprise providing a fluid that comprises a weighted elastomer. Theweighted elastomer may comprise an elastomer and a weighting agentattached to an outer surface of the elastomer. The weighted agent maycomprise a material selected from the group consisting of pumicite,perlite, and a combination thereof. The method further may compriseintroducing the fluid into a subterranean formation.

The features and advantages of the present invention will be readilyapparent to those skilled in the art. While numerous changes may be madeby those skilled in the art, such changes are within the spirit of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

These drawings illustrate certain aspects of some of the embodiments ofthe present invention, and should not be used to limit or define theinvention.

FIG. 1 is an illustration of a weighted elastomer in accordance with oneembodiment of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention relates to weighted elastomers and, moreparticularly, in certain embodiments, to weighted elastomers, cementcompositions comprising weighted elastomers, and methods of usingweighted elastomers in cementing operations. As used herein, the term“weighted elastomer” refers to an elastomer that has been weighted tohave a specific gravity of at least about 1.1. One of the many potentialadvantages of the methods and compositions of the present invention maybe that the inclusion of the weighted elastomer in embodiments of thecement compositions may reduce problems associated with segregation,especially when used in combination with weighting agents, as only theneed to address additives with specific gravities greater than water maybe needed.

An embodiment of the cement compositions of the present inventioncomprises cement, water, and a weighted elastomer that comprises anelastomer and a weighted agent attached to an outer surface of theelastomer. In certain embodiments, the cement compositions further maycomprise a weighting agent. Those of ordinary skill in the art willappreciate that embodiments of the cement compositions generally shouldhave a density suitable for a particular application. By way of example,embodiments of the cement compositions may have a density of about 4pounds per gallon (“lb/gal”) to about 20 lb/gal. In certain embodiments,the cement compositions may have a density of about 8 lb/gal to about 17lb/gal. In certain embodiments, the cement composition may be aheavyweight cement composition having a density of at least about 14lb/gal. Those of ordinary skill in the art, with the benefit of thisdisclosure, will recognize the appropriate density for a particularapplication.

Hydraulic cement is a component that may be included in embodiments ofthe cement compositions of the present invention. Any of a variety ofhydraulic cements suitable for use in subterranean cementing operationsmay be used in accordance with embodiments of the present invention.Suitable examples include hydraulic cements that comprise calcium,aluminum, silicon, oxygen and/or sulfur, which set and harden byreaction with water. Such hydraulic cements, include, but are notlimited to, Portland cements, pozzolana cements, gypsum cements,high-alumina-content cements, slag cements, silica cements andcombinations thereof. In certain embodiments, the hydraulic cement maycomprise a Portland cement. The Portland cements that may be suited foruse in embodiments of the present invention are classified as Class A,C, G, and H cements according to American Petroleum Institute, APISpecification for Materials and Testing for Well Cements, APISpecification 10, Fifth Ed., Jul. 1, 1990. In addition, in someembodiments, hydraulic cements suitable for use in the present inventionmay include cements classified as ASTM Type I, II, or III.

The water used in embodiments of the cement compositions of the presentinvention may include, for example, freshwater, saltwater (e.g., watercontaining one or more salts dissolved therein), brine (e.g., saturatedsaltwater produced from subterranean formations), seawater, orcombinations thereof. Generally, the water may be from any source,provided, for example, that it does not contain an excess of compoundsthat may undesirably affect other components in the cement composition.In some embodiments, the water may be included in an amount sufficientto form a pumpable slurry. In some embodiments, the water may beincluded in the cement compositions of the present invention in anamount of about 40% to about 200% by dry weight of cementitiouscomponents (“bwoc”). In some embodiments, the water may be included inan amount of about 40% to about 150% bwoc.

A weighted elastomer may be included in embodiments of the cementcompositions of the present invention. The weighted elastomer maycomprise, for example, an elastomer and a weighted agent attached to anouter surface of the elastomer. As illustrated in FIG. 1, weightedelastomer 10 may comprise elastomer 20 and weighting agent 30 attachedto an outer surface 40 of the elastomer, in embodiments of the presentinvention. The weighted elastomer is generally heavier than elastomersthat have been used heretofore, in that the weighted elastomer has beenweighted to a specific gravity of at least about 1.1. Of their manypotential advantages, one such advantage of using the weighted elastomeris that segregation issues associated with using elastomers may bereduced or even eliminated. For example, when using the weightedelastomer in combination with a weighting agent, problems associatedwith using an elastomer that floats and a weighting agent that sinksshould generally be avoided.

The weighted elastomer may be added to embodiments of the cementcomposition by dry blending with the cement before the addition of thewater, by mixing with the water to be added to the cement, or by mixingwith the cement composition consecutively with or after the addition ofthe water. Moreover, the weighted elastomer may be included inembodiments of the cement compositions in an amount desired for aparticular application. In some embodiments, the weighted elastomer maybe present in an amount of about 0.1% to about 100% bwoc (e.g., about1%, about 5%, about 10%, about 20%, about 30%, about 40%, about 50%,about 60%, about 70%, about 80%, about 90%, etc.). In certainembodiments, the weighted elastomer may be present in an amount of about1% to about 30% bwoc and, alternatively, in an amount of about 5% toabout 25% bwoc.

Any of a variety of elastomers may be weighted to form the weightedelastomers in accordance with embodiments of the present invention.Generally, the elastomers may be used in particulate form. As usedherein, the term “particulate” refers to materials in solid state havinga well-defined physical shape as well as those with irregulargeometries, including any particulates elastomers having the physicalshape of platelets, shavings, fibers, flakes, ribbons, rods, strips,spheroids, hollow beads, toroids, pellets, tablets, or any otherphysical shape. Examples of suitable elastomers, include, but are notlimited to, polypropylene, polyethylene, styrene divinyl benzene,polyisoprene, polybutadiene, polyisobutylene, polyurethane,styrene-butadiene random and block copolymers, acrylonitrile-butadiene,and acrylonitrile-styrene-butadiene.

In certain embodiments, the elastomer may be a swellable elastomer. Asused herein, an elastomer is characterized as swellable when it swellsupon contact with oil and/or swells upon contact with aqueous fluids. Byway of example, the elastomer may be an oil-swellable elastomer that itswells upon contact with any of a variety of oils, such as crude oil,diesel oil, kerosene and the like, as well as, oil-based fluids and gasor liquid hydrocarbons located in subterranean foimations. By way offurther example, the elastomer may be a water-swellable elastomer thatswells upon contact with aqueous fluids, such as fresh water, salt waterand the like, as well as, water-based fluids and aqueous fluids locatedin subterranean formations. Among other things, use of a swellableelastomer in embodiments of the cement compositions may help maintainzonal isolation, for example, by swelling when contacted by oil and/oraqueous fluids to seal cracks in the cement sheath and/or micro-annulusbetween the cement sheath and the pipe string or formation that may becreated.

Swellable elastomers suitable for use in embodiments of the cementcompositions may generally swell by up to about 500% of their originalsize at the surface. Under downhole conditions, this swelling may bemore or less depending on the conditions presented. For example, theswelling may be at least 10% at downhole conditions. In someembodiments, the swelling may be up to about 200% under downholeconditions. However, as those of ordinary skill in the art, with thebenefit of this disclosure, will appreciate, the actual swelling whenthe swellable elastomer is included in a cement composition may vary,for example, based on the concentration of the swellable elastomerincluded in the cement composition and the amount of oil and/or aqueousfluid present, among other factors.

Oil-swellable elastomers that should be used in embodiments of theweighted elastomer include any of a variety of materials that swell uponcontact with oil. Some specific examples of suitable oil-swellableelastomers include, but are not limited to, natural rubber, polyurethanerubber, nitrile rubber, hydrogenated nitrile rubber, acrylate butadienerubber, polyacrylate rubber, butyl rubber, brominated butyl rubber,chlorinated butyl rubber, chlorinated polyethylene rubber, isoprenerubber, choloroprene rubber, neoprene rubber, butadiene rubber, styrenebutadiene copolymer rubber, sulphonated polyethylene, ethylene acrylaterubber, epichlorohydrin ethylene oxide copolymer rubber,ethylene-propylene-copolymer (peroxide cross-linked),ethylene-propylene-copolymer (sulphur cross-linked),ethylene-propylene-diene terpolymer rubber, ethylene vinyl acetatecopolymer, fluoro rubbers, fluoro silicone rubbers, silicone rubbers,poly 2,2,1-bicyclo heptene (polynorborneane), alkylstyrene, andcrosslinked substituted vinyl acrylate copolymers. Combinations ofoil-swellable elastomers may also be used. Other elastomers that behavein a similar fashion with respect to oil also may be suitable. Those ofordinary skill in the art, with the benefit of this disclosure, will beable to select an appropriate oil-swellable elastomer for use in thecompositions of the present invention based on a variety of factors,including the application in which the composition will be used and thedesired swelling characteristics.

Water-swellable elastomers that should be used in embodiments of theweighted elastomer include any of a variety of materials that swell uponcontact with water. Some specific examples of water-swellable elastomersinclude, but are not limited to, super-absorbent polymers (such aspolymethacrylate and polyacrylamide) and non-soluble acrylic polymers(such as starch-polyacrylate acid graft copolymer and salts thereof),polyethylene oxide polymers, carboxymethyl cellulose type polymers,poly(acrylic acid) and salts thereof, poly(acrylic-co-acrylamide) andsalts thereof, graft-poly(ethylene oxide) of poly(acrylic acid) andsalts thereof, poly(2-hydroxyethyl methacrylate), poly(2-hydroxypropylmethacrylate), polyvinyl alcohol cyclic acid anhydride graft copolymer,isobutylene maleic anhydride, vinylacetate-acrylate copolymer, andstarch-polyacrylonitrile graft copolymers. Combinations ofwater-swellable elastomers may also be suitable. Other elastomers thatbehave in a similar fashion with respect to aqueous fluids also may besuitable. Those of ordinary skill in the art, with the benefit of thisdisclosure, will be able to select an appropriate water-swellableelastomer for use in the compositions of the present invention based ona variety of factors, including the application in which the compositionwill be used and the desired swelling characteristics.

Embodiments of the swellable elastomers may be dual oil/water swellable,in that the elastomer may comprise a combination or mixture of bothoil-swellable and water-swellable materials. A particle is characterizedas “dual oil/water-swellable” when it swells upon contact with oil andalso swells upon contact with aqueous fluids. In accordance withembodiments of the present invention, the oil-swellable material and/orthe water-swellable material may comprise an elastomer. By way ofexample, the swellable elastomer may comprise an ethylene-propylenepolymer (e.g., ethylene-propylene copolymer rubber orethylene-propylene-diene terpolymer rubber). and bentonite. By way offurther example, the swellable elastomer may comprise a butyl rubber andsodium bentonite.

As previously described, the weighted elastomer is an elastomer that hasbeen weighted to have a specific gravity of at least about 1.1 (e.g.,about 1.5, about 2, about 2.5, about 3, about 3.5, about 4, about 4.5,about 5). Alternatively, the elastomer may be weighted to have aspecific gravity of at least about 2, at least about 3, or at leastabout 4. One of ordinary skill in the art will be able to recognize asuitable specific gravity of the weighted elastomer for a particularapplication.

An example of a suitable weighted elastomer may comprise an elastomerand a weighting agent attached to an outer surface of the elastomer. Byway of example, a plurality of particles of the weighting agent may beattached to the outer surface of the elastomer. Weighting agents aretypically materials that weigh more than water and may be used toincrease the density of a cement composition. By way of example,weighting agents may have a specific gravity of at least 2 (e.g., about2, about 4, etc.). Examples of weighting agents that may be usedinclude, but are not limited to, pumicite, perlite, hematite,hausmannite, barite, sand (e.g., silica flour), cement, and combinationsthereof. In one embodiment, the perlite includes non-expanded perlite.Specific examples of suitable weighting agents include HI-DENSE®weighting agent, available from Halliburton Energy Services, Inc., andSSA-1™ cement additive, available from Halliburton Energy Services, Inc.In an embodiment, the abrasiveness of the weighting agent may be onefactor to consider when selecting a material for weighting theelastomer. Weighting agents that are less abrasive may be desired, incertain embodiments, to reduce or even avoid potential damage to theelastomer during manufacture of the weighted elastomer. In anembodiment, pumicite and/or perlite may be selected to weight theelastomer over a more abrasive material, such as barite.

The amount of the weighting agent used in embodiments of the weightedelastomers generally may depend on a number of factors, including theparticular elastomer, the desired specific gravity for the elastomer,the particular weighting agent, and the specific end-use application. Incertain embodiments, the weighted elastomer may have a weight ratio ofthe weighting agent to the elastomer of about 99:1 to about 0.1:1 and,alternatively, a weight ratio of about 3:1 to about 1:1.

The weighting agent generally may have a particle size that is smallerthan the particle size of the elastomer. By way of example, theweighting agent may have a particle size that is less than or equal toabout 50% of the particle size of the elastomer. In certain embodiments,the weighting agent may have a particle size that is less than or equalto about 10% of the particle size of the elastomer and, alternatively,less than or equal to about 5% of the particle size of the elastomer.

While the weighting agent may be attached to the outer surface of theelastomer, the weight agent generally should not fully coat theelastomer in certain embodiments of the present invention. In otherwords, at least a portion of the surface of the elastomer should remainuncovered, in certain embodiments, after attachment of the weightingattachment. This may be desirable, for example, so that the elastomer(e.g., a swellable elastomer) can come into contact with fluids afterplacement into a well bore. In certain embodiments, at least about 1% toabout 99% (e.g., about 5%, about 10%, about 25%, about 50%, about 75%,etc.) of the surface of the elastomer portion of the weighted elastomermay be uncovered.

The weighting agent may be attached to the elastomer using any suitabletechnique. By way of example, the weighting agent may be attached to theouter surface of the elastomer with an adhesive. Any of a variety ofadhesives that can adhere the weighting agent to the outer surface ofthe elastomer may be suitable. Examples of suitable adhesives mayinclude, but are not limited to, water-based acrylic paints, oil-basedpaints, and oil-based primers.

A variety of techniques may be used for attaching the weighting agent tothe elastomer with an adhesive. For example, the elastomer may first bemixed with the adhesive to at least partially coat the elastomer withthe adhesive. This mixture may then be passed through a sieve to removelarge pieces of the elastomer. The weighting agent may then be combinedwith this mixture such that the adhesive attaches the weighting agent tothe outer surface of the elastomer. In another embodiment, the weightingagent (rather than the elastomer) may first be mixed with the adhesiveto at least partially coat the weighting agent with the adhesive. Theelastomer may then be combined with this mixture such that the adhesiveattaches the weighting agent to the outer surface of the elastomer.Thereafter, the mixture may be passed through a sieve to remove largepieces. If desired, additional weighting material may then be added tothe mixture.

While embodiments may provide for attaching a weighting agent to theelastomer, one or more additional weighting agents may be included inembodiments of the cement compositions of the present invention. Itshould be understood that this weighting agent is separate from, and maybe the same or different than, the weighting agent that may be attachedto the elastomer. As previously described, weighting agents aretypically materials that weigh more than water and may be used toincrease the density of a cement composition. By way of example,weighting agents may have a specific gravity of at least 2 (e.g., about2, about 4, etc.). Examples of weighting agents that may be usedinclude, but are not limited to, pumicite, perlite, hematite,hausmannite, barite, sand (e.g., silica flour), cement, and combinationsthereof. Specific examples of suitable weighting agents includeHI-DENSE® weighting agent, available from Halliburton Energy Services,Inc., and SSA-1™ cement additive, available from Halliburton EnergyServices, Inc.

The weighting agent may be added to embodiments of the cementcomposition by dry blending with the cement before the addition of thewater, by mixing with the water to be added to the cement, or by mixingwith the cement composition consecutively with or after the addition ofthe water. Where used, the weighting agent may be included in the cementcomposition in an amount sufficient to, for example, provide the desireddensity. By way of example, the weighting agent may be included in anamount of about 0.1% to about 150% bwoc, alternatively, in an amount ofabout 10% to about 70% bwoc, and alternatively, in an amount of about15% to about 50% bwoc.

Other additives suitable for use in subterranean cementing operationsalso may be added to embodiments of the cement compositions, inaccordance with embodiments of the present invention. Examples of suchadditives include, but are not limited to, strength-retrogressionadditives, set accelerators, set retarders, weighting agents,lightweight additives, gas-generating additives, mechanical propertyenhancing additives, lost-circulation materials, filtration-controladditives, dispersants, fluid loss control additives, defoaming agents,foaming agents, thixotropic additives, and combinations thereof.Specific examples of these, and other, additives include crystallinesilica, amorphous silica, fumed silica, salts, fibers, hydratable clays,calcined shale, vitrified shale, microspheres, fly ash, slag,diatomaceous earth, metakaolin, rice husk ash, natural pozzolan,zeolite, cement kiln dust, lime, resins, latex, combinations thereof,and the like. A person having ordinary skill in the art, with thebenefit of this disclosure, will readily be able to determine the typeand amount of additive useful for a particular application and desiredresult.

In accordance with embodiments of the present invention, a method of thepresent invention may comprise providing a cement composition comprisingcement, water, and a weighted elastomer, and allowing the cementcomposition to set. As will be appreciated, the cement composition maybe allowed to set in any suitable location where it may be desired forthe cement composition to set into a hardened mass. By way of example,the cement composition may be allowed to set in a variety of locations,both above and below ground.

Additionally, embodiments of the cement compositions of the presentinvention may be used in a variety of subterranean applications wherecement compositions may be used, including, but not limited to, primarycementing, remedial cementing, and drilling operations. An example of amethod of the present invention may comprise introducing a cementcomposition that comprises cement, water, and a weighted elastomer intoa subterranean formation; and allowing the cement composition to set inthe subterranean formation. As desired by one of ordinary skill in theart, with the benefit of this disclosure, embodiments of the cementcompositions of the present invention useful in this method may compriseany of the above-listed additives, as well any of a variety of otheradditives suitable for use in subterranean application. Placing thecementing composition in the subterranean formation is intended toencompass placement of the cement composition in a well bore and/orplacement of the cement composition in rock surrounding the well borewith the well bore penetrating the subterranean formation. In exampleprimary cementing embodiments, a cement composition may be introducedinto a space between a subterranean formation and a conduit (e.g.,casing, expandable casing, liners, etc.) located in the subterraneanformation. The cement composition may be allowed to set to form ahardened mass in the space between the subterranean formation and theconduit. Generally, in most instances, the hardened mass should fix theconduit in the formation. The method further may comprise, for example,introducing the conduit into the subterranean formation. In addition, inexample remedial cementing embodiments, a cement composition may used,for example, in squeeze cementing operations (e.g., to seal voids and/orholes in the formation, cement sheath, and/or a pipe) or in theplacement of cement plugs.

While the preceding discussion is directed to the use of a weightedelastomer in cementing methods, those of ordinary skill in the art willappreciate that the present technique also encompasses the use ofweighted elastomers in a variety of different subterranean treatments,including drilling fluids, completing fluids, stimulation fluids, spacerfluids, and well clean-up fluids. In accordance with one embodiment, aweighted elastomer may be included in a spacer fluid. For example, aspacer fluid may be placed between two fluids contained in or to bepumped within a well bore. Examples of fluids between which spacerfluids are utilized include between cement compositions, and drillingfluids, between different drilling fluids during drilling fluid changeouts and between drilling fluids and completion brines. Among otherthings, spacer fluids may be used to enhance drilling fluid and filtercake removal from the walls of well bores, to enhance displacementefficiency and to physically separate chemically incompatible fluids.For example, a hydraulic cement composition and a drilling fluid may beseparated by a spacer fluid when the cement composition is placed in thewell bore. In accordance with embodiments of the present invention, thespacer fluid may prevent, or at least partially reduce, intermixing ofthe cement composition and the drilling fluid and may facilitate theremoval of filter cake and gelled drilling fluid from the walls of thewell bore during displacement of the drilling fluid by the cementcomposition. In accordance with another embodiment, the weightedelastomer may be included in a drilling fluid. By way of example, amethod may comprise using a drill bit to enlarge a well bore; andcirculating a drilling fluid that comprises a weighted elastomer pastthe drill bit to remove cuttings.

To facilitate a better understanding of the present technique, thefollowing examples of some specific embodiments are given. In no wayshould the following examples be read to limit, or to define, the scopeof the invention.

Example 1

Example weighted elastomers were prepared in accordance with a firstprocedure following procedure. One hundred grams of an elastomer(WELLLIFE® 665 elastomer, available from Halliburton Energy Services,Inc.) were mixed with 120 cubic centimeters of an adhesive (water-basedpaint) until all of the elastomer was thoroughly and evenly coated. Thesample was then passed through a 16-mesh sieve to remove large pieces.Next, a sufficient amount of a weighting agent (HI-DENSE® weightingagent, available from Halliburton Energy Services, Inc.) was mixed withthe sample to thoroughly and evenly coat the sample. Thereafter, thesample was passed through an 80-mesh sieve to remove excess weightingagent from the sample. The portion of the sample collected on the sievewas then dried in a vacuum overnight at 175° F. After drying, the samplewas cooled to room temperature, and the specific gravity was measuredusing an Ultrapycnometer 1000 by Quantachrome Instruments. A portion ofthe dried sample was then washed with water on an 80-mesh sieve toremove any of the weighting agent that was not sufficiently adhered tothe sample. Next, the sample was again dried in a vacuum overnight at175° F. After drying, the sample was cooled to room temperature, and thespecific gravity was again measured. The difference between the specificgravity after sieving and drying and the specific gravity after washingand drying was recorded. From this specific gravity change, theadherence of the weighting agent to the elastomer can be analyzed. Theabove procedure was repeated using an oil-based paint as the adhesive.

Additional weighted elastomers were prepared in accordance with a secondprocedure. Two hundred grams of a weighting agent (HI-DENSE® weightingagent, available from Halliburton Energy Services, Inc.) were mixed with100 grams of an adhesive (oil-based primer) until all of the weightingagent was thoroughly and evenly coated. One hundred grams of anelastomer (WELLLIFE® 665 additive, available from Halliburton EnergyServices, Inc.) were then mixed with the sample until a homogenousmixture was obtained. Thereafter, the sample was passed through a16-mesh sieve to remove large pieces. Additional weighting agent wasadded to the sieved sample and blended until the sample was evenlycoated with the weighting agent. The sample was then passed through an80-mesh sieve to remove excess weighting agent from the sample. Thesample collected on the sieve was then dried in a vacuum overnight at175° F. After drying, the sample was cooled to room temperature, and thespecific gravity was measured using an Ultrapycnometer 1000 byQuantachrome Instruments. A portion of the dried sample was then washedwith water on an 80-mesh sieve to remove any of the weighting agent thatwas not sufficiently adhered to the sample. Next, the sample was againdried in a vacuum overnight at 175° F. After drying, the sample wascooled to room temperature, and the specific gravity was again measured.The difference between the specific gravity after sieving and drying andthe specific gravity after washing and drying was recorded. From thisspecific gravity change, the adherence of the weighting agent to theelastomer can be analyzed.

The results of the specific gravity measurements for the three differentadhesives are provided in the table below.

TABLE 1 Specific Gravity Specific Gravity Specific Prepa- After SievingAfter Washing Gravity Adhesive ration and Drying (g/cc) and Drying(g/cc) Change Water-Based Procedure 1.8914 1.8175 0.0739 Acrylic Paint#1 Oil-Based Procedure 1.8835 1.8650 0.0185 Paint #1 Oil-Based Procedure2.1889 2.1740 0.0149 Primer #2

Based on the results shown in Table 1, a weighted elastomer may beprepared by attaching a weighting agent to the outer surface of theelastomer. From this table, it can also be observed that secondpreparation procedure using the oil-based primer resulted in a weightedelastomer with a higher specific gravity than for the first preparationprocedure.

Example 2

The following series of tests were performed to evaluate the mechanicalproperties of cement compositions that comprise a weighted elastomer. Asset forth below, the test results demonstrate that inclusion of aweighted elastomer in the cement composition results in a set cementhaving properties suitable for particular cementing applications.

Sample Cement Composition No. 1 (comparative) comprised Lehigh Class Acement and 35% bwoc of SSA-1™ cement additive. SSA-1™ cement additive issilica flour available from Halliburton Energy Services, Inc. Thissample composition did not include the weighted elastomer. This samplehad a density of 17.28 lb/gal.

Sample Cement Composition No. 2 comprised Lehigh Class A cement, 35%bwoc of SSA-1™ cement additive, 0.5% bwoc of CFR-3™ cement frictionreducer, 2% bwoc of bentonite, 8% bwoc of a weighted elastomer, and 4.56gallons of water per 94-pound sack of cement. CFR-3™ cement frictionreducer is available from Halliburton Energy Services, Inc. The weightedelastomer included in this sample composition was a weighted elastomerprepared in accordance with the second procedure of Example 1 using theoil-based primer as an adhesive. This sample had a density of 17.12lb/gal.

Sample Cement Composition No. 3 comprised Lehigh Class A cement, 35%bwoc of SSA-1™ cement additive, 0.5% bwoc of CFR-3™ cement frictionreducer, 2% bwoc of bentonite, 16% bwoc of a weighted elastomer, and4.54 gallons of water per 94-pound sack of cement. The weightedelastomer included in this sample composition was a weighted elastomerprepared in accordance with the second procedure of Example 1 using theoil-based primer as an adhesive. This sample had a density of 17.12lb/gal.

After the sample compositions were prepared, tests were performed todetermine the compressive strength, Young's Modulus, and Poisson's ratioassociated with each composition. The compressive strength tests wereperformed at room temperature in accordance with API Specification 10.The Young's modulus and Poisson's ratio were statically deteiiuined bymeans of compression testing using a load frame. The Young's modulus (ormodulus of elasticity) for each sample composition was obtained bytaking a ratio of a simple tension stress applied to each sample to aresulting strain parallel to the tension in that composition. ThePoisson's ratio for each sample was determined by calculating a ratio oftransverse strain to a corresponding axial strain resulting fromuniformly distributing axial stress below a proportional limit of eachsample. The Young's Modulus and Poisson's ratio were determined usingASTM D3184-02 and ASTM D2464-95a. The values determined for each samplecomposition are provided in the table below.

TABLE 2 Sample 4-Day Cement Weighted Confining Compressive Compo-Elastomer Pressure Strength Young's Poisson's sition (% bwoc) (psi)(psi) Modulus Ratio No. 1 0 0 17,221 3.34E+06 0.208 No. 2 8 0 11,6232.63E+06 0.217 No. 3 16 0 8,447 2.30E+06 0.199

Additional tests were performed on four different samples of each of thesample cement compositions to determine the Brazilian tensile strength.The Brazilian tensile strength was determined at room temperature inaccordance with ASTM D3967496-96. The density of the set cement was alsodetermined. The values determined for each sample composition areprovided in the table below.

TABLE 3 Brazilian Sample Weighted Tensile Cement Elastomer StrengthDensity Composition Sample (% bwoc) (psi) (lb/gal) No. 1 A 0 1,454 17.61No. 1 B 0 1,330 17.65 No. 1 C 0 1,384 17.72 No. 1 D 0 1,428 17.82 No. 2A 8 421 17.29 No. 2 B 8 534 17.33 No. 2 C 8 522 17.30 No. 2 D 8 55317.30 No. 3 A 16 582 17.06 No. 3 B 16 474 17.15 No. 3 C 16 629 17.08 No.3 D 16 385 17.07

The average Brazilian tensile strengths and densities for tested samplesfor each of the four sample cement compositions are provided in thetable below.

TABLE 4 Sample Cement Weighted Elastomer Brazilian Tensile DensityComposition (% bwoc) Strength (psi) Variation No. 1 0 1,399 1.2% No. 2 8508 0.2% No. 3 16 518 0.5%

Based on the results of these tests, a cement composition comprising aweighted elastomer may have properties suitable for particularapplications.

Therefore, the present invention is well adapted to attain the ends andadvantages mentioned as well as those that are inherent therein. Theparticular embodiments disclosed above are illustrative only, as thepresent invention may be modified and practiced in different butequivalent manners apparent to those skilled in the art having thebenefit of the teachings herein. Although individual embodiments arediscussed, the invention covers all combinations of all thoseembodiments. Furthermore, no limitations are intended to the details ofconstruction or design herein shown, other than as described in theclaims below. It is therefore evident that the particular illustrativeembodiments disclosed above may be altered or modified and all suchvariations are considered within the scope and spirit of the presentinvention. While compositions and methods are described in terms of“comprising,” “containing,” or “including” various components or steps,the compositions and methods can also “consist essentially of” or“consist of” the various components and steps. Whenever a numericalrange with a lower limit and an upper limit is disclosed, any number andany included range falling within the range is specifically disclosed.In particular, every range of values (of the form, “about a to about b,”or, equivalently, “from approximately a to b,” or, equivalently, “fromapproximately a-b”) disclosed herein is to be understood to set forthevery number and range encompassed within the broader range of values.Also, the terms in the claims have their plain, ordinary meaning unlessotherwise explicitly and clearly defined by the patentee.

What is claimed is:
 1. A weighted elastomer comprising: an elastomer;and a weighting agent attached to an outer surface of the elastomer,wherein the weighting agent comprises a material selected from the groupconsisting of pumicite, perlite, and a combination thereof, wherein theweighting agent is attached to the outer surface of the elastomer usingan adhesive, wherein the adhesive comprises at least one adhesiveselected from the group consisting of a water-based acrylic paint, anoil-based paint, and an oil-based primer, wherein the weighted elastomerhas a specific gravity of at least about 1.1.
 2. The weighted elastomerof claim 1 wherein the elastomer comprises an elastomer selected fromthe group consisting of polypropylene, polyethylene, styrene divinylbenzene, polyisoprene, polybutadiene, polyisobutylene, polyurethane, astyrene-butadiene random copolymer, a styrene-butadiene block copolymer,acrylonitrile butadiene, acrylonitrile-styrene-butadiene, and anycombination thereof.
 3. The weighted elastomer of claim 1 wherein theelastomer comprises a styrene-butadiene block copolymer.
 4. The weightedelastomer of claim 1 wherein the elastomer comprises a swellableelastomer, and wherein the weighting agent does not fully coat theswellable elastomer.
 5. The weighted elastomer of claim 4 wherein theswellable elastomer comprises an oil swellable elastomer selected fromthe group consisting of natural rubber, polyurethane rubber, nitrilerubber, hydrogenated nitrile rubber, acrylate butadiene rubber,polyacrylate rubber, butyl rubber, brominated butyl rubber, chlorinatedbutyl rubber, chlorinated polyethylene rubber, isoprene rubber,choloroprene rubber, neoprene rubber, butadiene rubber, styrenebutadiene copolymer rubber, sulphonated polyethylene, ethylene acrylaterubber, epichlorohydrin ethylene oxide copolymer rubber,ethylene-propylene-copolymer that is peroxide cross-linked,ethylene-propylene-copolymer that is sulphur cross-linked,ethylene-propylene-diene terpolymer rubber, ethylene vinyl acetatecopolymer, a fluoro rubber, a fluoro silicone rubber, a silicone rubber,poly 2,2,1-bicyclo heptene (polynorborneane), alkylstyrene, crosslinkedsubstituted vinyl acrylate copolymer, and any combination thereof. 6.The weighted elastomer of claim 4 wherein the swellable elastomercomprises a water swellable elastomer selected from the group consistingof polymethacrylate, polyacrylamide, a non-soluble acrylic polymer,starch-polyacrylate acid graft copolymer and salts thereof, apolyethylene oxide polymer, a carboxymethyl cellulose type polymer,poly(acrylic acid) and salts thereof, poly(acrylic-co-acrylamide) andsalts thereof, graft-poly(ethylene oxide) of poly(acrylic acid) andsalts thereof, poly(2-hydroxyethyl methacrylate), poly(2-hydroxypropylmethacrylate), polyvinyl alcohol cyclic acid anhydride graft copolymer,isobutylene maleic anhydride, vinylacetate-acrylate copolymer,starch-polyacrylonitrile graft copolymer, and any combination thereof.7. The weighted elastomer of claim 4 wherein the swellable elastomer isdual oil/water swellable and comprises an oil-swellable material and awater-swellable material.
 8. The weighted elastomer of claim 1 whereinthe weighting agent comprises the perlite.
 9. The weighted elastomer ofclaim 1 wherein the weighting agent comprises the pumicite.
 10. Theweighted elastomer of claim 1 wherein the weighted elastomer has aspecific gravity of at least about 1.5.
 11. The weighted elastomer ofclaim 1 wherein a weight ratio of the weighting agent to the elastomeris about 3:1 to about 1:1.
 12. A weighted elastomer comprising: anelastomer selected from the group consisting of polypropylene,polyethylene, styrene divinyl benzene, polyisoprene, polybutadiene,polyisobutylene, polyurethane, a styrene-butadiene random copolymer, astyrene-butadiene block copolymer, acrylonitrile butadiene,acrylonitrile-styrene-butadiene, and any combination thereof; and aweighting agent attached to an outer surface of the elastomer, whereinthe weighting agent comprises a material selected from the groupconsisting of pumicite, perlite, and a combination thereof, wherein theweighting agent is attached to the outer surface of the elastomer usingan adhesive, wherein the adhesive comprises at least one adhesiveselected from the group consisting of a water-based acrylic paint anoil-based paint, and an oil-based primer, wherein a weight ratio of theweighting agent to the elastomer is about 3:1 to about 1:1, and whereinthe weighted elastomer has a specific gravity of at least about 1.1. 13.The weighted elastomer of claim 12 wherein the elastomer comprises astyrene-butadiene block copolymer.
 14. The weighted elastomer of claim12 wherein the weighting agent comprises the perlite.
 15. The weightedelastomer of claim 12 wherein the weighting agent comprises thepumicite.
 16. A weighted elastomer comprising: a swellable elastomer,and a weighting agent attached to an outer surface of the elastomer,wherein the weighting agent comprises a material selected from the groupconsisting of pumicite, perlite, and a combination thereof, wherein theweighting agent is attached to the outer surface of the elastomer usingan adhesive, wherein the adhesive comprises at least one adhesiveselected from the group consisting of a water-based acrylic paint, anoil-based paint, and an oil-based primer, wherein the weighted elastomerhas a specific gravity of at least about 1.1.
 17. The weighted elastomerof claim 16 wherein the swellable elastomer comprises an oil swellableelastomer selected from the group consisting of natural rubber,polyurethane rubber, nitrile rubber, hydrogenated nitrile rubber,acrylate butadiene rubber, polyacrylate rubber, butyl rubber, brominatedbutyl rubber, chlorinated butyl rubber, chlorinated polyethylene rubber,isoprene rubber, choloroprene rubber, neoprene rubber, butadiene rubber,styrene butadiene copolymer rubber, sulphonated polyethylene, ethyleneacrylate rubber, epichlorohydrin ethylene oxide copolymer rubber,ethylene-propylene-copolymer that is peroxide cross-linked,ethylene-propylene-copolymer that is sulphur cross-linked,ethylene-propylene-diene terpolymer rubber, ethylene vinyl acetatecopolymer, a fluoro rubber, a fluoro silicone rubber, a silicone rubber,poly 2,2,1-bicyclo heptene (polynorborneane), alkylstyrene, crosslinkedsubstituted vinyl acrylate copolymer, and any combination thereof. 18.The weighted elastomer of claim 16 wherein the swellable elastomercomprises a water swellable elastomer selected from the group consistingof polymethacrylate, polyacrylamide, a non-soluble acrylic polymer,starch-polyacrylate acid graft copolymer and salts thereof, apolyethylene oxide polymer, a carboxymethyl cellulose type polymer,poly(acrylic acid) and salts thereof, poly(acrylic-co-acrylamide) andsalts thereof, graft-poly(ethylene oxide) of poly(acrylic acid) andsalts thereof, poly(2-hydroxyethyl methacrylate), poly(2-hydroxypropylmethacrylate), polyvinyl alcohol cyclic acid anhydride graft copolymer,isobutylene maleic anhydride, vinylacetate-acrylate copolymer,starch-polyacrylonitrile graft copolymer, and any combination thereof.19. The weighted elastomer of claim 16 wherein the swellable elastomeris dual oil/water swellable and comprises an oil-swellable material anda water-swellable material.
 20. The weighted elastomer of claim 16wherein the swellable elastomer comprises a dual oil/water swellableelastomer selected from the group of ethylene-propylene copolymer andbentonite, ethylene-propylene-diene terpolymer and bentonite, butylrubber and sodium bentonite, and any combination thereof.